1. Field of the Invention
This invention generally relates to an apparatus and method for measuring caloric consumption. In particular, the invention relates to a caloric consumption measuring device and caloric consumption measuring method configured to measure a caloric consumption of a user based on a heart rate of the user detected while the user is performing an activity.
2. Background Information
A known apparatus exists which measures a caloric consumption of a user during exercise using a correlation between a heart rate and an oxygen intake quantity (e.g., Japanese Laid-Open Patent Publication No. 9-56705). This known caloric consumption measuring device has a correlation table that expresses a pre-calculated correlation line in terms of the heart rate and the oxygen intake quantity. The heart rate and an acceleration are obtained from an output of a heart rate sensor and used to determine an exercise intensity, and the oxygen intake quantity is calculated using the correlation table and the exercise intensity. Since an oxygen intake quantity of 3.5 ml/kg/min corresponds to a caloric consumption of 1 kcal/min, the caloric consumption during exercise can be calculated if the oxygen intake quantity and the amount of time exercised are known.
The correlation table is contrived such that the slope of the heart rate versus oxygen intake quantity correlation line is changed depending on whether the exercise load is high or low, thus enabling the caloric consumption to be measured under various exercise loads. However, the caloric consumption measuring device does not take into account such personal differences as the age, sex, weight, and physical strength of the user and it is possible for an error to be incurred due to such differences.
Meanwhile, a known caloric consumption measuring device exists which takes into account personal differences (e.g., Japanese Laid-Open Patent Publication No. 2002-336216). This known caloric consumption measuring device is configured to measure a reference heart rate at a normal activity state for which the energy metabolic rate is known and calculate a reference caloric consumption for the normal activity state based on the known energy metabolic rate and a coefficient determined based on the age, weight, and sex of the user. A regression equation is then found for the calculated reference caloric consumption and the reference heart rate, and a caloric consumption corresponding to a heart rate occurring during exercise is calculated using the obtained regression equation. There are also cases in which two regression equations, one corresponding to an exercising state and one corresponding to a resting state, are used to calculate a caloric consumption.
The caloric consumption measuring device described above calculates the caloric consumption using a regression equation obtained based on actual exercise and enables the caloric consumption to be calculated in accordance with physical strength differences and other personal physical condition differences that exist among users. However, this approach incurs the disadvantage that the calculation of the regression equation is limited to an exercise (normal activity) for which the energy metabolic rate is known. Additionally, with this approach, in order to calculate the regression equation, the exercise for which the energy metabolic rate is known must actually be performed in order to obtain the reference heart rate and the reference caloric consumption. Thus, when the user will perform various types of exercise, a reference heart rate and a reference caloric consumption must be found for each exercise and the measurement of caloric consumption becomes complex.